Stretch-activated ion channels in growth cones of snail neurons

Using single-channel recording, we show that neurons contain ion channels sensitive to membrane tension. Neurons isolated from the snail, Lymnaea stagnalis, actively rearborized in culture yielding cell bodies and growth cones suitable for patch clamping. All neurons contained, in both their soma and growth cones (at a density of approximately 1-2 micron-2), stretch-activated channels highly selective for K+. The presence of this mechanosensitive channel in the motile region of the neuron, a region characterized by insertion of new membrane--the growth cone--is of particular interest. Under physiological conditions, the channel was permeable to K+, but not to Na+ or Cl-. Its conductance to K+ under these conditions was approximately 44 pS. Channel activation was steeply dependent on membrane tension, showing thresholds at between -50 to -100 mm Hg (suction was applied through the recording pipette). Kinetic analysis indicated that the stretch-dependent increase in the channel's open probability was related to a long closed state rather than to one of the open states. Given the importance of Ca2+ in the regulation of growth cone motility, we speculate that this stretch-activated K+ channel could play a role in neurite elongation by a tension-dependent modulation of membrane voltage which in turn would act on voltage-gated Ca2+ channels.